What Can Superconducting Gravimeters Contribute to Normal-Mode Seismology?
The seismic free oscillations of the Earth can be observed in the frequency band from 0.3 to 20 mHz, and estimates of their frequencies constitute the principal constraints for spherically symmetric Earth models such as the Preliminary Reference Earth Model (PREM). While the bulk of the mode observations rely on recordings of the spring gravimeters deployed in the International Deployment of Accelerometers (IDA) network and more recently on the Streckiesen STS-1 seismometers deployed in the global seismic network (GSN), we show here that the most recent generation of superconducting gravimeters (SGs) can achieve lower noise levels than either one of the aforementioned sensors at frequencies lower than ∼0.8 mHz. While the splitting of modes above 1 mHz is largely due to structural heterogeneities in P- and S-wave velocities, the modes below 1 mHz are unique for two reasons: (1) the destabilizing effect of self-gravitation leads to a high sensitivity to density heterogeneities and (2) th
